1. Field of the Invention
The invention relates to compositions for use in repelling insects. The compositions can be applied to humans, animals, vegetation, or embedded into various materials. Specifically, the insect repellent composition of the invention includes only naturally occurring repellent substances. The invention also relates to special methods for preparing such compositions.
2. Description of Related Art
Insect repellents have been used for centuries to prevent insects from annoying humans and animals alike. Repellents have also been used to prevent insect harm to such items as food, clothing, and furniture. Some examples of known repellents include citronella candles made from citronella oil, and moth balls, which contain chemicals (camphor, para-dichlorobenzene, Napthalene) and/or cedar wood. Over the last century, synthetic chemicals have been developed that more effectively repel insects. Some of these synthetic chemicals include 2-ethyl-3-hexanediol, DDT and DEET (N,N-diethyl toluamide).
However, most synthetic chemical repellents, especially DEET, can be readily absorbed through the skin, causing many accidental poisonings, especially of children. They also can poison wildlife. DDT in particular has been shown to be very harmful to the environment, and DEET is suspected to be a carcinogen, teratogen and/or mutagen. Most of these synthetic chemicals are toxic in certain amounts. Therefore, some states have limited the percentage of synthetic toxic chemicals, especially DEET (e.g. to levels of 10-30%), which may be included in any formulation for human or animal use.
A further concern is that insects can develop a genetic resistance to many synthetic chemicals used in insect repellents and insecticides. Through natural selection, each generation of insect is less effected by any chemical widely used in its area than was the previous generation. Therefore, stronger concentrations or larger amounts of these synthetic chemicals are needed each year in order to control insect populations. In the case of DEET and other synthetic chemicals, particularly known or suspected mutagens, carcinogens and teratogens, these larger doses are undesirable because of the possible deleterious effects on humans, fish, birds, animals and, possibly, vegetation. Further, many of them are nonbiodegradable.
Therefore, another, preferably non-toxic or less toxic, means of repelling insects is desired. Many natural substances are known to repel insects, but these are normally only effective for a short period of time. Further, many natural substances lose their effectiveness when formulated for human or animal use through refining and processing into lotions, oils, sprays and other like substances.
However, it has been found that combinations of various substances that are extracted from vegetable matter by cold processing such as expeller pressing, rolling or centrifugation, for example, form a more effective insect repellent with an efficacy the same as or greater than that of synthetic chemicals such as DEET.
It is known that various naturally occurring substances work as insect repellents and/or insecticides in nature. In particular, the essential oils of various plants repel certain insects and are not believed to cause genetic mutations in insects. Therefore, no resistance to these natural substances should be developed by insects.
These oils can be extracted by many different processes, such as by the use of solvents, steam distillation, use of an expeller, pressurization or centrifugation. However, the processes of solvent extraction and steam distillation are the ones most often used commercially because of their higher yields, lower cost or process simplicity.
One of the most frequently used natural insect repellents is Margosa oil (Neem oil), which yields azadirachtin in large quantities during steam distillation or solvent extraction. Azadirachtin is generally considered desirable for use in large amounts, and is frequently used in insecticide compositions and in low levels for repellency. However, there are some compositions wherein the azadirachtin is removed after solvent extraction, as in U.S. Pat. No. 5,372,817 to Locke et al.
However, many substances that also repel insects other than azadirachtin are present in cold processed extracted oils. For example, other materials yielded from the Margosa (Neem) tree also possess insect repellent properties of equal or greater value than azadirachtin. However, these other substances are not yielded, or are yielded in very small quantities, by the commercially favored processes of steam distillation and solvent extraction.
In contrast, cold expeller pressing, pressurization and ultra-centrifugation yield these substances in large amounts, while often producing less azadirachtin. This is true when performing cold processing extractions on other plants as well--vital substances are recovered by such expeller pressing, pressurization and centrifugation that are otherwise lost in solvent extraction and steam distillation. Temperatures above 60.degree. can destroy many of these active substances.